Lessons I have learned, often the hard way....
If you shop around for prices via the travel sites (expedia, travelocity, etc.) you are going to find that the prices will all be about the same. They track where you have been and how often you check back for ticket prices. The more often you check, the less likely you will get a good deal.
The best deals that I have received have been directly from the airlines themselves. Check the other sites for the flight and airline options, select a few and then CALL the airlines individually. They will do much better over the phone than over the internet, especially with group rates. When you call, and get a quote, ask for a quote number so that if you call back you can reference it to get the same price. Note that they will often tell you that the quotes are only good for about 24 hrs so you need to go about this in one sitting.
Lastly, as passedpawn has indicated above, shop about 6 weeks ahead of your trip. The more of a particular flight they can fill up early, the less discounting they do the later weeks.
Saturday is usually discounted quite a bit. Most business people fly out on Sunday/Monday and return on Thursday/Friday, so it is harder to get cheaper flights then. The airlines will hold out for the higher fares on those days.
All in all, it's a pretty sucky way to do business, but what can you do when you need to fly...